I managed to integrate the write-magic function from bubba-buttond into the sysinitv package . The result is a shutdown command that will properly bring the B3 to its 'powered off' state. This package is now available in the bubba overlay for gentoo. Since this package changes the behaviour of the halt command in a way that it will no longer work on other systems, I've added a hardware check that prevents the package from being installed on systems that do not run the Kirkwood Feroceon SoC. While you may circumvent that check by altering a USE flag, this will also kee the hardware specific patches from being deployed and thus install a normal version of sysinitv.